The present invention relates generally to the detection of extravasation of fluids injected into a patient, and, more particularly, to extravasation detection apparatuses, systems and methods in medical injection procedures using energy transmission through tissue in the vicinity of an injection site or other site.
In many medical diagnostic and therapeutic procedures, a physician or other person injects a patient with a fluid. In recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of contrast medium in procedures such as angiography, computed tomography, ultrasound and NMR/MRI have been developed.
Extravasation is the accidental infusion of an injection fluid such as a contrast medium into tissue surrounding a blood vessel rather than into the blood vessel itself. Extravasation can be caused, for example, by fragile vasculature, valve disease, inappropriate needle placement, or patient movement resulting in the infusing needle being pulled from the intended vessel or causing the needle to be pushed through the wall of the vessel. Furthermore, high injection pressures and/or rates of some modern procedures increase the risk of extravasation. In computed tomography, for example, contrast injection flow rates can be in the range of 0.1 to 10 ml/s.
Moreover, extravasation can cause serious injury to patients. In that regard, certain injection fluids such as contrast media or chemotherapy drugs can be toxic to tissue if not diluted by blood flow. It is, therefore, very important when performing fluid injections to detect extravasation as soon as possible and discontinue the injection upon detection.
Several extravasation techniques are known in the art. Two simple and very useful techniques for detecting extravasation are palpation of the patient in the vicinity of the injection site and simple visual observation of the vicinity of the injection site by a trained health care provider. In the palpation technique, the health care provider manually senses swelling of tissue near the injection resulting from extravasation. By visual observation, it is also sometimes possible to observe directly any swelling of the skin in the vicinity of an injection site resulting from extravasation.
In addition to palpation and observation, there are a number of automated methods of detecting extravasation that may include automatic triggering of an alarm condition upon detection. Unfortunately, each of these automated methods of detecting extravasation is limited by significant drawbacks.
U.S. Pat. No. 4,647,281, for example, discloses subcutaneous temperature sensing of extravasation to trigger an alarm. In this method of extravasation detection, an antenna and a microwave radiometer instantaneously measure the temperature of the subcutaneous tissue at the site where fluid is injected. An algorithm periodically determines the temperature difference between the tissue and the injected fluid, and compares the difference to a fixed threshold. An alarm processor uses the comparison to determine an alarm condition.
In addition, U.S. Pat. No. 5,334,141 discloses a microwave extravasation detection system employing a reusable microwave antenna and a disposable attachment element for releasably securing the microwave antenna to a patient's skin over an injection site. The attachment element holds the antenna in intimate contact with the patient's skin to optimize microwave transfer therebetween, while shielding the antenna from environmental noise signals. Although measurement of temperature changes and emissivity using microwave energy can result in instantaneous detection, temperature differences are often too small for practical measurement.
Several plethysmographic detection techniques are available in addition to known temperature sensing techniques. For example, mercury strain gauge plethysmographs measure the volume change resulting from venous blood flow in a cross-sectional area of a limb of a patient. Air cuff or pulse volume recorder plethysmographs measure the changes in pressure within a recording cuff caused by the change in volume of a limb or digit as a result of extravasation. Such plethysmographs can be cumbersome to operate and/or insensitive to small changes in volume.
Photo-plethysmographs measure the optical scattering properties of capillary blood to detect the presence of extravasated fluids in tissue. An example of a photo-plethysmograph is described in U.S. Pat. No. 4,877,034. Because light is heavily absorbed in tissue, however, the sensitivity of photo-plethysmographs is generally limited to the top ¼ inch to ½ inch of tissue. Most extravasations, however, occur deeper than ¼ inch to ½ inch. Moreover, the injection medium may flow into interstitial spaces remote from the photo-plethysmograph sensors and go undetected.
Impedance plethysmographs measure changes in the electrical impedance in a defined tissue volume of a limb. In this method, an impedance change of a certain level in the vicinity of the injection site is interpreted as being an extravasation. A change in impedance occurs during extravasation because injection fluid in the tissue of the patient changes both the volume and the electrical impedance properties of the tissue. Use of electrodes in impedance plethysmographs can, however, result in instabilities. For example, maintaining suitable electrical contact between the electrodes of impedance plethysmographs and the skin of the patient is often very difficult.
It is, therefore, very desirable to develop improved devices and methods for detecting extravasation during, for example, the high flow rate procedures (1 to 10 ml/sec) typically encountered in angiographic, CT, ultrasound, and MR imaging procedures.